SMS 1586 Metric O-Rings

SMS 1586 O-Ring Size Identification

The SMS 1586 system identifies O-rings using two fundamental dimensions:

ID = Inside Diameter

C/S = Cross Section

For example, an O-ring may be specified using a dimensional combination such as:

25 × 2.5 mm

where:

• 25 mm = nominal inside diameter
• 2.5 mm = nominal cross-section

The approximate free-state outside diameter can then be estimated as:

OD ≈ ID + 2 × C/S

Therefore:

OD ≈ 25 + 2(2.5) = 30 mm

This calculation is useful when checking an O-ring against a physical component, but the calculated OD should not be used as a substitute for the applicable dimensional tolerances.

Why ID and Cross-Section Must Both Be Checked

A common purchasing mistake is to identify an O-ring only by its inside diameter.

For example, two seals might both have an ID of approximately 25 mm:

• 25 × 2.0 mm
• 25 × 2.5 mm

These are not interchangeable simply because their inside diameters are identical.

Changing the cross-section changes the relationship between the O-ring and the gland.

It can affect:

• Squeeze
• Groove fill
• Contact pressure
• Assembly force
• Extrusion resistance
• Friction
• Dynamic wear
• Pressure capability

For this reason, an SMS 1586 replacement should always be verified using both ID and cross-section.

How to Read an SMS 1586 O-Ring Dimension

Suppose a drawing identifies an O-ring by:

ID × C/S

The interpretation is straightforward:

Inside Diameter × Cross Section

For example:

40 × 3 mm

means:

• Inside diameter = 40 mm
• Cross-section = 3 mm

Approximate outside diameter:

40 + 2 × 3 = 46 mm

This gives the nominal free-state geometry.

However, the actual installed geometry depends on the gland.

The O-ring may be compressed radially or axially during installation, meaning its free-state OD is not the same as its installed sealing geometry.

Can an SMS 1586 O-Ring Be Replaced With a Generic Metric O-Ring?

Yes, in some applications.

But the replacement should be evaluated based on the actual gland rather than the name of the size standard.

For a low-risk static application, a dimensionally equivalent generic metric O-ring may be perfectly suitable.

For a high-pressure dynamic hydraulic application, however, the engineering requirements are considerably stricter.

The more demanding the application, the less appropriate it becomes to use a simple “same size” substitution.

SMS 1586 O-Rings and Groove Design

An O-ring does not seal because the rubber ring is simply “the right size.”

It seals because the ring is correctly positioned and compressed inside a gland.

The groove determines:

• Compression
• Contact pressure
• Available expansion space
• Extrusion clearance
• Thermal expansion behavior
• Assembly conditions

This is why a dimensionally correct O-ring can still leak if installed in an incorrectly designed groove.

Material Selection for SMS 1586 O-Rings

SMS 1586 identifies the size and application group, not a universal elastomer compound.

The same dimensional O-ring can potentially be manufactured from:

• NBR
• FKM
• EPDM
• Silicone
• HNBR
• FVMQ
• FFKM
• AFLAS
• Other engineered elastomers

Therefore, an RFQ should never simply state:

“SMS 1586 O-ring.”

Instead, specify the material whenever the application is known.

SMS 1586 O-Ring Failure Modes

Leakage After Installation

Potential causes include:

• Incorrect ID
• Incorrect cross-section
• Wrong groove dimensions
• Insufficient squeeze
• Damaged O-ring
• Incorrect installation
• Contaminated sealing surfaces

Extrusion Damage

Typical appearance:

• Small pieces missing from the O-ring
• Nibbling along the pressure side
• Torn elastomer

Potential causes:

• Excessive pressure
• Excessive clearance
• Soft material
• Excessive temperature

Compression Set

The O-ring remains permanently flattened after removal.

Possible causes:

• Excessive temperature
• Long service time
• Incorrect compound
• Excessive compression
• Poor material selection

Swelling

The O-ring becomes larger or softer.

Possible causes:

• Fluid incompatibility
• Solvent exposure
• Incorrect elastomer

The solution is usually material correction, not simply changing the O-ring size.

Cracking

Possible causes include:

• Excessive heat
• Ozone exposure
• Chemical attack
• Aging
• Incorrect compound

Abrasion

Abrasion is especially important in dynamic applications.

Possible causes:

• Poor surface finish
• Excessive friction
• Insufficient lubrication
• Excessive speed
• Incorrect material
• Incorrect squeeze

This is one reason the SMS 1586 D/S classification should be considered when selecting a replacement.

How to Write an SMS 1586 O-Ring RFQ

For purchasing departments, the following format is much more useful than providing only a size.

Recommended RFQ Information

Standard: SMS 1586
Classification: D or S
ID: XX mm
Cross-section: X.X mm
Material: NBR / FKM / EPDM / etc.
Hardness: XX Shore A
Fluid: Actual working medium
Temperature: Minimum / continuous / maximum
Pressure: Operating / peak
Application: Static / reciprocating / rotary
Quantity: Required quantity
Certification: If applicable

For example:

SMS 1586 D, 25 × 2.5 mm, NBR 70 Shore A, hydraulic oil, −20°C to +100°C, dynamic hydraulic application.

This gives the manufacturer significantly more useful information than:

“25 × 2.5 SMS 1586 O-ring.”

Final Engineering Guide to SMS 1586 O-Rings

The most useful way to understand SMS 1586 is as a metric O-ring identification system that combines dimensional information with a practical distinction between dynamic/static and primarily static applications.

The standard identifies O-rings primarily by:

Inside Diameter + Cross Section

and separates them into:

D = Dynamic + Static

S = Mainly Static

This makes SMS 1586 especially valuable when working with older Swedish or European machinery where the original sealing specification may still appear on engineering drawings and maintenance documentation.

But the size reference should never be treated as a complete O-ring specification.

A successful replacement requires the complete chain:

SMS 1586 size → ID → C/S → D/S classification → groove → material → hardness → fluid → temperature → pressure → motion → installation

That is the key distinction between finding an O-ring that fits and finding an O-ring that will continue to seal.

For low-risk static applications, dimensional replacement may be relatively straightforward.

For dynamic hydraulic, pneumatic, high-temperature, chemically aggressive, or high-pressure applications, the selection process must go further. The engineer should verify the groove, surface condition, elastomer compatibility, hardness, extrusion clearance, lubrication, and operating conditions before approving a cross-reference.

When an SMS 1586 O-ring is no longer readily available, DIN 3771, ISO 3601, BS 4518, JIS B 2401, and generic metric sizes can provide useful comparison points, but none should be accepted solely because the nominal dimensions appear similar. Global O-Ring’s international reference material demonstrates that multiple metric and imperial O-ring standards coexist and are commonly used for cross-reference work.

The best procurement specification is therefore not simply:

“SMS 1586 O-ring.”

It is:

“SMS 1586 + exact ID/C/S + D or S classification + material + hardness + operating conditions.”

That approach reduces incorrect substitutions, improves spare-parts management, minimizes repeat leakage, and gives manufacturers enough information to supply an O-ring that is appropriate for the actual sealing application.